While African women in Darfur were being raped by the Janjaweed militiamen, Arab women stood nearby and sang for joy, according to an Amnesty International report published yesterday. The songs of the Hakama, or the "Janjaweed women" as the refugees call them, encouraged the atrocities committed by the militiamen.

The women singers stirred up racial hatred against black civilians during attacks on villages in Darfur and celebrated the humiliation of their enemies, the human rights group said.

"[They] appear to be the communicators during the attacks. They are reportedly not actively involved in attacks on people, but participate in acts of looting."

Amnesty International collected several testimonies mentioning the presence of Hakama while women were raped by the Janjaweed. The report said:"Hakama appear to have directly harassed the women [who were] assaulted, and verbally attacked them."

During an attack on the village of Disa in June last year, Arab women accompanied the attackers and sang songs praising the government and scorning the black villagers.

According to an African chief quoted in the report, the singers said: "The blood of the blacks runs like water, we take their goods and we chase them from our area and our cattle will be in their land. The power of [Sudanese president Omer Hassan] al-Bashir belongs to the Arabs and we will kill you until the end, you blacks, we have killed your God."

The chief said that the Arab women also racially insulted women from the village: "You are gorillas, you are black, and you are badly dressed."

The Janjaweed have abducted women for use as sex slaves, in some cases breaking their limbs to prevent them escaping, as well as carrying out rapes in their home villages, the report said.

The militiamen "are happy when they rape. They sing when they rape and they tell that we are just slaves and that they can do with us how they wish", a 37-year-old victim, identified as A, is quoted as saying in the report, which was based onmore than 100 testimonies from women in the refugee camps in neighbouring Chad.

Pollyanna Truscott, Amnesty International's Darfur crisis coordinator, said the rape was part of a systematic dehumanisation of women. "It is done to inflict fear, to force them to leave their communities. It also humiliates the men in their communities."

The UN estimates that up to 30,000 people have been killed in Darfur, and more than a million have been forced to flee their homes. Peace talks between the Sudanese government and two rebel movements broke down on Saturday when the rebel groups walked out, saying the government must first disarm the Janjaweed.

Another human rights organisation, Human Rights Watch, today publishes alleged Sudanese government documents showing that it was much more closely involved with the Janjaweed than it has so far admitted.

The documents, which Human Rights Watch said it had obtained from the civilian administration in Darfur and are dated February and March this year, call for "provisions and ammunition" to be delivered to known Janjaweed militia leaders, camps and "loyalist tribes".

One document orders all security units in the area to tolerate the activities of Musa Hilal, the alleged Janjaweed leader in north Darfur interviewed by the Guardian last week.

Peter Takirambudde, the executive director of Human Rights Watch's Africa division, said: "These documents show that militia activity has not just been condoned, it's been specifically supported by Sudan government officials."

The official government line is that it did not arm or support the Janjaweed, though its presence was useful in helping to combat rebels in Darfur.